The predecessor of the present complex structure was begun in the spring of 1558 by Pope Paul IV in the Vatican Gardens, west of the Cortile del Belvedere.
Paul IV commissioned the initial project of the 'Casina del Boschetto', as it was originally called, from an unknown architect; the first mention of the single-storey building can be found on 30 April 1558, and a notice of the following 6 May, says that the Pope spent "two thirds of his time at the Belvedere, where he has begun to build a fountain in the woods".
The complex, as it was completed in 1562, comprised an elliptical cortile, two free-standing portals, and the loggia with its fountain.
[2] The Casina's rich and at times obscure iconographic programme, of the efficacy of baptism, the primacy of the papacy and the welcomed punitive powers of the Church,[3] seems to have been inspired by Cardinal Charles Borromeo, nephew of Pius IV, who probably had it in mind as the headquarters for the Academy he was about to found, on 20 April 1562, called Accademia Noctes Vaticanae.
Graham Smith[2] suggests that the interrelated iconography of the interior frescoes was inspired by Cardinal Marcantonio da Mula.